Micro Electro-Mechanical Systems (MEMS) accelerometers typically consist of a pendulous proof mass, a suspension system (flexures) and a method for determining the relative motion of the proof mass under the influence of acceleration (F=MA). Surviving high shock environments while maintaining performance necessary for navigation purposes imposes significant obstacles on Micro Electro-Mechanical Systems (MEMS) accelerometers. Very small MEMS accelerometers are required in order to survive high shock environments. Flexure systems for MEMS accelerometers must be designed to limit motion to a unique sensing axis. The flexure suspension must minimize the effects from environmental stress and strain while possessing enough strength to permit operation in high shock environments. Historically, strain isolation is required on these types of devices to isolate the sensor from mounting strains. The strains experienced are typically due to the thermal coefficient of expansion (TCE) difference between the device material and the mounting material.
Single axis, pendulous, capacitive-sensing MEMS accelerometers are extremely popular for high shock environments at a low cost. Their small overall geometry is ideal for high shock packages that require minimum size. FIG. 1 illustrates torsional flexures that are used to support a pendulous mass for one of these accelerometers. Thus, unwanted twisting occurs. Also, the torsional flexures sag from the weight of the pendulous mass, thereby introducing an error source.
Therefore, there is an unmet need for a pendulous MEMS accelerometer with improved pendulous support and greater isolation from mechanical strains.